In an internal combustion engine, generally known ignition systems for ignition of an air-fuel mixture includes an ignition system having an auxiliary electrode apart from main electrodes.
For example, such an ignition system having the auxiliary electrode has been conventionally proposed, which includes a center electrode and a ground electrode as an electrical configuration for discharging, and a microwave radiation antenna as an electrical configuration for introducing and radiating a microwave (for example, see Patent Document 1).
Also, another ignition system is known, which includes a negative electrode for an electric discharge, and a first positive electrode and a second positive electrode respectively having different inter-electrode distances relative to the negative electrode. In such a configuration, a voltage is applied between the negative electrode and the first positive electrode having a shorter inter-electrode distance so as to detect the electric discharge, then a voltage is applied between the negative electrode and the second positive electrode having a longer inter-electrode distance. Thus, the discharge can be performed between the long inter-electrode distance from the negative electrode to the second positive electrode (for example, see Patent Document 2).
Furthermore, another ignition system is proposed, which includes a high-voltage main electrode and a main ground electrode to perform an arc discharge, and auxiliary electrodes to generate, before performing the arc discharge, a plasma atmosphere in a discharge region (for example, see Patent Document 3).